The invention concerns a head clamp for positioning a head, with a frame formed from two frame elements, which respectively have first ends which are movably joined together and second ends which carry pins for fixing the head in position.
In the case of the already known head clamps of the type initially described, the head is clamped between the two frame elements, i.e., by a linear movement of the two frame elements relative to one another. For the purpose of positioning the head, it is first brought between the two frame elements and the two frame elements are then moved axially towards one another by means of a side arm of each of the frame elements. The frame elements are locked relative to one another for the purpose of initial fixing in position. The head is finally clamped by means of a fine adjustment of the pins in which the latter are moved yet further on to the head.
The disadvantages of these head clamps are to be seen primarily in the large amount of mechanical play of the frame elements relative to one another; the longer the side arms that are in contact with one another, the greater is this play. Moreover, the adjustment and retightening of the pins by screwing is demanding and awkward. Also disadvantageous is the increased risk of breakage with increased loading, particularly through the attachment of additional appliances. These head clamps are also unsuitable for additional neuroradiological examinations, since they substantially restrict the beam path.
Accordingly, the object of the present invention is to develop a head clamp of the generic type in such a way that a greater mechanical stability is achieved.
This object is achieved, in the case of a head clamp of the type initially described, according to the invention in that the frame elements are pivoted relative to one another about a common axis of rotation.
For the purpose of clamping the head, the two frame elements are swivelled relative to one another, about a common axis of rotation. This enables the frame elements to be dimensioned as small as possible since, unlike those of head clamps which are adjustable in the axial direction, the side arms of the frame elements do not have to be made longer in order to permit opening of the head clamp. Due to the relative swivelling of the frame elements, a maximum opening angle can consequently be set with a very small structural size. This facilitates the handling and the application of the head clamp. In addition, the weight of the head clamp is drastically reduced, since the frame elements can be made substantially smaller and shorter. Due to a smaller structural form of the head clamp achieved thus, its mechanical stability is increased substantially in comparison with those already known in the art.
According to a preferred embodiment of the present invention, provision can be made such that the frame comprises a swivel position fixing device with at least one fixing component, on one of the two frame elements, which has at least one projection, and with corresponding recesses, disposed on the other frame element, in which the projection engages in a fixing position and fixes the frame elements in their position relative to one another, and that the fixing component can be brought relative to the recesses from the fixing position into a release position in which the frame elements can be swivelled relative to one another.
This design of the head clamp enables the frame elements to be fixed in a defined position relative to one another. It is thus possible to define the relative swivelling of the frame elements solely through the interaction of the fixing component with the recesses, for example, solely through the movement of the projection of the fixing component into the recess. As soon as the fixing component is withdrawn from the recesses, the frame elements can be swivelled again as required.
It is then advantageous if the recesses are connected non-rotatably to the other frame element. The non-rotatable connection has the advantage, firstly, of making the position fixing as free of play as possible, since a relative degree of freedom for a movement between the recesses and the frame element of the head clamp is thus eliminated. In addition, there is no need for a further, complicated, locking mechanism since the projections of the fixing components of the one frame element engage directly in the recesses and, in this way, are joined directly to the other frame element.
It is particularly advantageous if the fixing component is movable relative to both frame elements. The fixing component that is movably joined to the one frame element can thus engage in the recesses of the other frame element and remain invariably joined to the one frame element.
According to an advantageous embodiment, there can be provision such that the fixing component can be moved by means of an actuating component joined to it with a positive fit. The advantage lies in the fact that the fixing component can be concealed. Only the actuating component need be accessible to a person operating the head clamp. In addition, to facilitate actuation of the fixing component, an appropriate lever is provided on the actuating component. Furthermore, it is conceivable that one or more fixing components can be moved by a single actuating component. A quick-action mechanism is thus achieved for the head clamp.
In the case of another preferred embodiment of the invention, provision can be made such that the fixing component is mounted on a frame element in such a way that it can be moved towards the recesses. The swivelled head clamp can thus be fixed in its position solely by the fixing component being pushed into the recess. This renders possible particularly fast and easy handling of the head clamp.
In the case of another embodiment of the invention, provision can be made such that the fixing component is mounted on the one frame part in such a way that it can be swivelled towards the recesses. A pivoted mounting of the fixing component allows levers, resulting from this type of mounting, to be used on the fixing component, rendering possible a particularly force-efficient locking or release by means of the fixing component.
It is particularly advantageous if the recesses are formed by the teeth of a toothed wheel whose circumference extends maximally over an angular range of 360xc2x0. Toothed wheels can be produced very simply and cost-effectively by machine. In addition, it can be sufficient to provide only a limited angular range of the toothed wheel with teeth for which fixing of the head clamp in its position is required. This also reduces the production expenditure.
It is then advantageous if the teeth are undercut on at least one side. This has the advantage that when the fixing component is engaged between the teeth of the toothed wheel, inadvertent removal of the fixing component from the recess becomes impossible if the head clamp is pretensioned. An additional safeguard is thus provided against unintentional release of the fixing position.
According to a preferred embodiment of the invention, provision can be made such that only one of the fixing components can be brought into the fixing position in each case. A more precise subdivision for possible swivel positions of the head clamp can thus be predefined with appropriate arrangement of the fixing components relative to the recesses. This means, firstly, that the number of fixing positions can be increased and, secondly, that the fixing components and the corresponding recesses can be made sufficiently large to permit an optimal transfer of force. In addition, the play of the frame elements in relation to one another is reduced and the mechanical stability of the head clamp is coincidentally increased.
It is advantageous if the projections on the fixing components are in each case offset, according to the number of fixing components by a fraction, which is the reciprocal of this number, of a tooth division of this toothed wheel. The number of teeth of the tooth wheel is thus in effect multiplied by a factor corresponding to the number of fixing components. This means, for example, that in the case of there being 20 teeth on a quarter-circle circumference and there being four fixing components, a possible number of 80 fixing positions is obtained. Instead of increasing the number of teeth and consequently reducing the size of the recesses, the teeth can be made larger, with the result that the stability of the head clamp is increased and greater forces can be taken up by the swivel position fixing device.
Provision can by made in principle such that the swivel position fixing device has at least one elastic pressure element which holds the fixing component in the fixing position. It is thus ensured that the frame elements stay fixed in position relative to one another. Consequently, it is then only necessary to move the fixing components when the frame elements are to be swivelled relative to one another.
Above all, this offers the safeguard that fixing of the frame elements in position is not forgotten. An operator wishing to swivel the head clamp into any desired position must first release all fixing components, for example by means of the actuating component. Otherwise, the fixing components are held in the recesses by the pressure element.
It is then advantageous if the elastic pressure element is formed by a leaf spring. A leaf spring can be produced cheaply and is simple to mount. In addition, a leaf spring has relatively large bearing faces. Several fixing components can thus also be held simultaneously in the fixing position by one leaf spring.
In the case of a preferred embodiment of the present invention, provision can be made such that all fixing components can be brought simultaneously into their release position by the actuating component. This provides for a rapid adjustment of the swivel position. If the actuating component is not actuated the fixing components lock in the recesses and the head clamp is fixed in a defined swivel position. It is only through actuation of the actuating component that all fixing components are brought simultaneously into their release position. The frame elements of the head clamp can then be swivelled relative to one another.
Provision can be made in principle such that a frame element has a frame part and a support part joined to the latter, that the frame part and the support part can be pivoted about the common axis of rotation and define a swivel angle and that the frame part can be fixed in position relative to the support part for each possible swivel angle. No further fine adjustment on the head clamp is possible by the fixing of a swivel position as described above by means of fixing components and corresponding recesses. Such a fine adjustment becomes possible only through the division of the frame element into the frame part and the support part. By contrast with the swivel position fixing device, each possible swivel angle can be fixed between the frame part and the support part. The pins can thus be brought into each possible position for locating a head.
Provision can then be made such that the frame part can be swivelled and fixed in position in a defined manner relative to the support part by means of a swivel angle adjusting device and that the swivel angle adjusting device can be adjusted by a screwed connection. The additional screwed connection enables the frame part to be both swivelled and fixed in position relative to the support part. The main advantage of this design is that fine adjustment of the head clamp is possible by means of a single screwed connection. Moreover, no further screwed connections are necessary.
It is particularly advantageous if the fixing components are disposed on the support part. The joining of the support part to the frame part enables the frame part to be swivelled relative to the other frame element. This swivel position is fixed by means of the fixing components disposed on the support part and the recesses disposed on the other frame element. The support part is thus fixed in its position relative to the other frame element. On this basis, the frame part can be swivelled and fixed in position relative to the support part by means of the screwed connection. Coarse setting of the head clamp is thus effected by means of a movement of the support part relative to the other frame element, fine adjustment being effected by means of a movement of the support part relative to the frame part joined to it.
Provision can be made in principle such that the frame elements have passage openings for a bearing shaft, defining the axis of rotation, and form a slide bearing with it. The sliding arrangement of the frame elements reduces to a minimum the tilt play transversely relative to the axis of rotation. In addition, the axis of rotation is defined by the axis of symmetry of the bearing shaft.
It is then advantageous if in the region of the bearing shaft the frame elements have slide faces, running transversely relative to the axis of rotation, by means of which they bear on one another. The frame elements can thus be supported on one another in the region of the axis of rotation. The sliding mounting without play on the bearing shaft and the slide faces bearing on one another can also reduce the tilt play.
It is particularly advantageous if a frame element is rigidly joined to the bearing shaft. An additional play between this frame element and the bearing shaft is thus rendered impossible at the outset, increasing the mechanical stability of the head clamp.
Provision can be made in principle such that the frame elements are fixed in position relative to one another in the direction of the axis of rotation. Thus, the frame elements cannot be separated from one another in the direction of the axis of rotation. This fixing can be used to set a required, if small, play between the frame elements and the bearing shaft, but only to the extent that there can be no tilting of the frame elements relative to one another.
According to a preferred embodiment of the invention, provision can be made in principle such that the frame elements are essentially L-shaped. This shape of the frame elements is particularly advantageous for optimally surrounding a head. In addition, the L-shape offers essentially two straight side sections to which further ancillary instruments can be attached.
It is advantageous if at the free end the one frame element has a pin whose longitudinal axis points essentially towards the free end of the other frame element. This alignment of the pin axis affords an optimal transfer of force from the frame element to the head via the pin.
It is advantageous if in that at its free end the other frame element has a rocker mounting whose longitudinal axis points essentially towards the free end of the other frame element, if the rocker mounting has an essentially C-shaped bow which is pivoted, transversely relative to its longitudinal axis, in its central region and if at each of its free ends the bow has a pin which points essentially towards the free end of the other frame element. Due to the shifting of the rough adjustment and fine adjustment to a base of the head clamp, it is no longer necessary to make the pins separately adjustable. Any required swivel angle between the frame elements can be compensated by means of the rocker mounting in such a way that the pin on the other frame element points exactly in each case towards the pivoted central region of the bow. It would also be conceivable for the rocker mounting to be mounted on the frame element so that it is rotatable about its longitudinal axis and can be fixed in any possible rotation position by means of a locking device. It is also possible to interchange the single pin with the rocker mounting, depending on the amount of space required for additional instruments having to be attached to the head clamp.
According to a preferred embodiment of the invention, provision can be made such that in cross section the frame elements have a profile which is shaped to complement the profile of a corresponding receiver of a standard mounting for further instruments. The head clamp thus becomes universally applicable for already existing mountings for positioning further instruments.
It is also advantageous if in the region of the axis of rotation the frame elements have on their respective exteriors a profile which is shaped to complement the profile of a receiver of a standardized head clamp holding device. Due to this special profiling, the head clamp can also be clamped into the head clamp holding devices already used for conventional head clamps. This enables the head clamps of the type initially described to be replaced by the newly proposed head clamps, using the existing head clamp holding devices.